Silane cure chemistry is used in different types of polymer technologies and compositions made therefrom, such as silylated acrylics, RTV silicones, silylated polyurethanes, silylated polyethers and others, for crosslinking. Such systems, when the backbones are organic polymers, are often referred to as hybrids, hybrid polymers, hybrid systems, or something similar since they can combine organic polymer chemistry with inorganic (silicon-based) cure chemistry. For this application RTV silicone systems are included in the compositions because they employ similar cure chemistry, even though they typically provide quite different cured properties. It is well known that the type of silane structure located on the polymer for crosslinking directly impacts the composition's properties, such as speed of cure, flexibility, adhesion or mechanical properties like tensile and tear strength at break.
Typical examples for the influence of the silane structure terminating the polymer chain on the system's properties after final cure are given for silylated urethane polymers e.g. in U.S. Pat. No. 4,374,237 to Berger, et al., where curable isocyanate-terminated polyurethanes are at least partially reacted with a secondary amine containing silane monomer having two trialkoxy silane groups. Other silane end-capped urethane polymers and sealants are disclosed in U.S. Pat. No. 3,627,722 to Seiter, which described polyurethane sealants such as alkylaminoalkyltrialkoxysilanes, mercaptoalkyltrialkoxysilanes, and arylaminoalkyltrialkoxysilanes containing a significant percentage, but preferably less than all, of terminal isocyanate groups endblocked with --Si(OR).sub.3, where R was a lower alkyl group.
To overcome the problem of insufficient flexibility, U.S. Pat. No. 4,645,816 to Pohl and Osterholtz teaches a novel class of room-temperature, moisture-curable, silane-terminated polyurethanes bearing terminal isocyanate groups reacted with a silane monomer having one dialkoxy silane group and an organo-functional group with at least one active hydrogen. The polymers are crosslinked to produce elastomeric networks with improved flexibility.
Another approach to reducing the crosslinking density of the cured elastomers, is to use secondary aminosilanes with bulky substituents on the nitrogen as silane endcappers, preferably reacting all free isocyanate endgroups with these secondary amino silanes. EP 676,403 to Feng reports that the use of arylaminosilanes, particularly having one dialkoxy silane group provided the added benefit of further improved flexibility. Zwiener, et al. disclosed in U.S. Pat. No. 5,364,955 similar benefits using certain N-alkoxysilylalkyl-aspartic acid esters. U.S. Pat. No. 4,345,053 to Rizk, et al., describes a moisture-curable silane-terminated polymer prepared by reacting a polyurethane having terminal active hydrogen atoms with an isocyanato organosilane having a terminal isocyanate group and at least one hydrolyzable alkoxy group bonded to silicon. U.S. Pat. No. 4,625,012 to Rizk and Hsieh, describes a moisture-curable polyurethane having terminal isocyanate groups and silane groups having at least one hydrolyzable alkoxy group bonded to silicon, in which the silane groups may be pendant to the chain.
Similar teaching is given for other silane cure hybrid systems. Linear and branched silane terminated polyether polymers are mixed in different ratios to vary flexibility and mechanical properties. RTV silicone crosslinker functionality leads to tailored physical properties.
Improved cure speed of silane terminated polyurethanes using a small amount of amino silane additives such as N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane has been shown in U.S. Pat. No. 3,979,344 by Bryant and Weis.